1. Field of the Invention
The present invention relates to optical fiber cross-connect switching.
2. Description of the Related Art
As optical fiber progressively supplements and replaces metal wire as the backbone of telecommunications networks, the switches that route optical signals have emerged as a significant bottleneck. Transmission systems move information as optical photons but the switching systems and so-called cross-connect fabrics that switch, route, multiplex, and demultiplex optical signals have generally been electronic. Electronic switching requires light to be converted to an electronic signal to pass through the switch and then be reconverted to light in a process termed optical-electronic-optical (OEO) conversion that introduces both time delay and cost.
There is great interest in the telecommunications industry, therefore, in developing all optical switching to avoid the necessity of multiple OEO conversions. As described, for example, by Bishop et al. in Scientific American (January, 2001, pp. 88-94), all optical switches based on a number of underlying technologies including Micro Electro Mechanical Systems (MEMS) tilting mirrors, thermo-optical devices, bubbles formed by inkjet printing heads, and liquid crystals, have been proposed. Optical fiber switches based on MEMS mirrors are particularly attractive because they can incorporate very large scale integrated circuits and can be robust, long-lived, and scalable.
An optical fiber switch described in U.S. Pat. No. 5,960,132 to Lin, for example, includes an array of hinged MEMS mirrors, each of which can be rotated about its hinge between a reflective state and a non-reflective state. An array of N2 such mirrors is required to switch signals carried by N input optical fibers from one to another of N output optical fibers. Unfortunately, N2 scaling results in unmanageably complex devices for large N.
Another optical fiber switch described in Bishop et al., cited above, as well as in Bishop et al., Photonics Spectra (March 2000, pp. 167-169) includes an array of MEMS mirrors disposed on a single surface. Each mirror tilts independently to direct light received from an array of input/output optical fibers to any other mirror and thus to any input/output fiber. This optical fiber switch does not appear to include optical diagnostics which would enable active closed-loop optical feedback control of the mirror orientations or allow input presence detection.
Optical fiber switches having a low insertion loss and capable of cross-connecting large numbers of input and output fibers would further the development of fiber optic telecommunications networks.